JP2015512061A - Multiphoton curing method using negative contrast composition - Google Patents

Abstract

The present disclosure relates to a multiphoton absorption method for curing a photocurable composition under conditions in which negative imaging occurs. This photocurable composition contains a compound capable of free radical polymerization. This method applies to the fabrication of structures on the micrometer scale or smaller.

Description

  The present disclosure relates generally to methods and materials for multi-photon photocuring.

  In typical multiphoton processes used to make two-dimensional (2D) and / or three-dimensional (3D) structures with micrometer scale or sub-micrometer scale resolution, the photocurable composition has a high strength. It is selectively cured using light, such as near infrared light provided by a near infrared (NIR) laser.

  In many known implementations, the photocurable composition includes one or more free radically polymerizable compounds (eg, acrylates and / or methacrylates). Photocurable compositions are generally less sensitive to near infrared wavelengths of light, but can be cured by simultaneous multiphoton absorption of non-linear light by a multiphoton photoinitiator system contained in the photocurable material. By this process, energy equivalent to about twice the light used is absorbed by the multiphoton photoinitiator system, which decomposes to produce free radicals, which are free radicals contained in the photocurable composition. Initiate free radical polymerization (typically involving crosslinking) of the polymerizable compound. Thus, at least partial curing of the photocurable composition occurs near the laser beam focus. The focal point of light is directed to various regions within the photocurable composition, thereby creating a latent structure within the photocurable composition. Next, the corresponding actual structure is made by removing areas of the photocurable composition that are not sufficiently cured (eg, solvent development).

  Multiphoton absorption (eg, free radical polymerization) that results in curing is highly dependent on the intensity and dose of light used, so a very small (eg, micrometer-scale or nanometer-scale) volume polymerization element (typically It is possible to create “voxels” (short for volume pixels). Typically, the focal point of the laser beam is an approximately ellipsoid with an intensity profile that is approximately Gaussian along an arbitrary diameter. Thus, a typical voxel produced by laser beam exposure may be approximately spherical or may resemble an elongated sphere, where the elongation is one or more axes (eg, x-axis, y-axis). Or the z-axis).

  Repeat for each voxel and build larger nanostructures and micrometer structures for the resin by controlling the focal position of the laser beam in three dimensions (ie, x-axis, y-axis, and z-axis directions). be able to. In many cases, a nearly single voxel layer (ie, the xy plane) is cured, followed by moving the focal point by about 1 voxel length (ie, on the z-axis) and the next layer (ie, xy). By curing the surface, a 3D structure is formed. This process can be repeated through a development step (eg, as described above) until the desired structure is formed.

  There is a continuing need for systems and methods that allow photolithography fabrication of high resolution micrometer and nanometer structures with smaller dimensions. We have found a way to achieve the above using free radical polymerizable materials in various conditions of negative imaging (ie causing a decrease in cure due to a stepwise increase in exposure).

In one aspect, the disclosure includes the following steps:
a) providing a light beam having a light beam cross-sectional profile comprising an inner region of relatively low light intensity surrounded by an outer region of relatively high light intensity, wherein The inner region and the outer region have the same temporal profile; and
b) providing a photocurable composition, the photocurable composition comprising a free radical polymerizable compound, a free radical polymerization inhibitor, and a multiphoton photoinitiator system; ,
c) By exposing at least a portion of the photocurable composition to light, multiphoton absorption by a multiphoton photoinitiator system of a portion of the light initiates free radical polymerization on at least a portion of the free radical polymerizable compound. Wherein irradiating the photocurable composition with at least a portion of the inner region of the light beam causes a portion of the photocurable composition to cure to at least a threshold level for development. And irradiating the photocurable composition with at least a portion of the outer region adjacent to the inner region of the light beam, the photocurable composition does not cure to at least a threshold level for development. A method comprising the steps of:

  In some embodiments, the photocurable composition further comprises an organic polymer that is substantially non-flowable. In some embodiments, the outer region of the beam cross-sectional profile is substantially annular. In some embodiments, the light beam comprises Gaussian Laguerre mode laser light. In some embodiments, the photocurable composition forms a layer disposed on the substrate. In some embodiments, the method further comprises developing at least a portion of the photocurable composition that has been cured (eg, polymerized and / or crosslinked) at least to a threshold level for development in step c). . In some embodiments, the free radical polymerization inhibitor comprises an organic free radical polymerization inhibitor. In some embodiments, the free-radically polymerizable compound includes at least two acryloyl groups.

In another aspect, the disclosure includes the following steps:
a) providing at least one light beam;
b) a step of providing a photocurable composition, the photocurable composition comprising a free radical polymerizable compound, a free radical polymerization inhibitor other than molecular oxygen, a multiphoton photoinitiator system, The free radical polymerization inhibitor is effective in the absence of oxygen, and
c) a portion of the photocurable composition is cured by exposure to at least one light beam, whereby the multiphoton absorption by the multiphoton photoinitiator system of a portion of the light is free radically polymerizable compound Initiate free radical polymerization and thereby reduce the degree of curing of at least a portion of the photocurable composition exposed to the light by a stepwise increase in exposure with the light, the photocurable composition Before the curable composition is exposed to the light, and is substantially free of molecular oxygen.

  In some embodiments, the free radical polymerizable compound comprises at least two methacryloyl groups, and the photocurable composition is substantially free of free radical polymerizable acrylates. In some embodiments, the photocurable composition further comprises an organic polymer and is substantially non-flowable. In some embodiments, the photocurable composition forms a layer disposed on the substrate. In some embodiments, the present light beam focuses at various locations within the photocurable composition according to a predetermined pattern.

In another aspect, the disclosure includes the following steps:
a) providing a light beam;
b) providing a photocurable composition, the photocurable composition comprising:
A compound capable of free radical polymerization;
A type I photoinitiator;
A process comprising a free radical polymerization inhibitor;
c) a compound capable of at least partially curing at least a portion of the photocurable composition by exposure to light, whereby multiphoton absorption of a portion of the light by a Type I photoinitiator is free radically polymerizable. Initiating free radical polymerization of the light, and thereby reducing the degree of curing of at least a portion of the photocurable composition exposed to the light by stepwise increasing the exposure with the light. To do.

  In some embodiments, the free radical polymerizable compound comprises at least one of a free radical polymerizable acrylate or a free radical polymerizable methacrylate.

  In some embodiments, the Type I photoinitiator is a substituted or unsubstituted benzoin ether, benzyl ketal, α, α-dialkoxyacetophenone, α-hydroxyalkylphenone, α-dialkylaminoalkylphenone, acylphosphine oxide. , Acylphosphine, substituted derivatives thereof, and combinations thereof. In some embodiments, the Type I photoinitiator comprises 2-benzyl-2- (dimethylamino) -4'-morpholinobutyrophenone.

  In the method described above, the photocurable composition can form a layer disposed on the substrate. In addition or alternatively, the photocurable composition may further comprise an organic polymer and may be substantially non-flowable.

  In the above method, step c) can be repeated a plurality of times. During each iteration, the light rays are focused at various locations within the photocurable composition according to a predetermined pattern, which can include predetermined pattern variations in each of the three dimensions. However, repeating step c) is not necessary to achieve the essential benefits of the present disclosure.

  Typically, the method described above further comprises developing at least a portion of the photocurable composition cured in step c) to at least a threshold level for development, although this is not essential.

  The method according to the present disclosure advantageously makes it possible to produce sub-micrometer shapes at practical laser scan speeds.

In this disclosure,
The term “free radical polymerization inhibitor” refers to a compound that inhibits free radical polymerization (eg, of free radical polymerizable acrylates and / or methacrylates).

  The term “light” refers to electromagnetic radiation ranging, for example, from about 300 nanometers (nm) to about 1500 nm.

  The term “(meth) acryl” refers to “acryl” and / or “methacryl”.

  The term “micrometer structure” means a 2D or 3D shape having at least one critical dimension that is less than about 800 micrometers (μm), typically less than about 500 micrometers, or even less than 100 micrometers. .

  The term “non-linear” with respect to light absorption refers to a process in which light absorption depends on a power greater than one.

  The term “multi-photon absorption” refers to a reactive electronic excitation in which two or more photons are absorbed simultaneously in a non-linear manner so that they are energetically inaccessible by the absorption of one photon of the same energy. Refers to reaching a state.

  The term “methacrylate compound” refers to a compound having at least one methacryloyl group.

  The terms “curing” and “photocuring” refer to the process of making a soluble photocurable composition (eg, a photoresist) insoluble by polymerization (eg, free radical polymerization, optionally with cross-linking). For example, if the termination of polymerization occurs before the degree of polymerization is sufficient to cause insolubilization, the polymerization can occur without curing (eg, insolubilization) of the photocurable composition.

The term “simultaneously” means two events that occur within a time period of 10 ⁻¹⁴ seconds or less.

  The features and advantages of the present disclosure will become better understood when considering the form for carrying out the invention and the appended claims.

1 is a schematic diagram of an exemplary system useful for performing a method according to the present disclosure. FIG. FIG. 6 is a schematic plot of vertical voxel dimensions versus reciprocal of writing speed at fixed multiphoton curing conditions for a hypothetical photocurable composition exhibiting negative contrast. It is a cross-sectional view of a Gauss-Laguerre mode _{TEM 01} ^* of the laser beam. ₁ is a cross-sectional view of a laser beam of a Gauss-Laguerre mode TEM ₁₀ . FIG. 3 is a schematic diagram of a two-dimensional 15-line pattern written by a laser under two-photon exposure conditions used to determine the threshold writing speed and voxel height in the z-direction in the examples. The z-axis position of the center line of the range is set at the wafer-photoresist interface. 3 is a graph showing contrast curves of Examples 1 and 2. It is a graph which shows the contrast curve of Example 3 and 4. It is a graph which shows the contrast curve of Example 3 and Comparative Example A. It is a graph which shows the contrast curve of Examples 5-7 and Comparative Example A. It is a graph which shows the contrast curve of Example 8 and Comparative Example A. It is a graph which shows the contrast curve of Example 2 and 9. 10 is a photomicrograph of a scanning electron microscope (SEM) showing a 3D shape generated by Example 10. FIG. 10 is a photomicrograph of a scanning electron microscope (SEM) showing a 3D shape generated by Example 10. FIG. 10 is a graph showing a contrast curve of Example 11.

  While several embodiments of the present disclosure have been described in the above drawings, other embodiments are possible, for example as described in the discussion. In all cases, this disclosure is presented by way of representation and not limitation. It should be understood that many other modifications and embodiments within the scope and spirit of the present disclosure can be devised by those skilled in the art. The figures may not be drawn to scale. Like reference numbers may be used throughout the figures to indicate like parts.

  Photocurable compositions useful in the practice of the present disclosure include a free-radically polymerizable compound, a multiphoton photoinitiator system, and typically a free radical polymerization inhibitor (eg, an organic free radical polymerization inhibitor, or And an inorganic free radical polymerization inhibitor (for example, oxygen).

  Examples of free-radically polymerizable compounds that can be used in one or more embodiments of the present disclosure include mono- and poly-acrylates and / or methacrylates, such as allyl acrylate, ethyl acrylate, isopropyl methacrylate, methyl acrylate. , Methyl methacrylate, n-hexyl acrylate, stearyl acrylate, 1,3-butylene glycol diacrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate, 1,4-butanediol diacrylate, 1, 4-cyclohexanedimethanol diacrylate, 1,4-cyclohexanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol monoacrylate monomethacrylate , Alkoxylated aliphatic diacrylate, alkoxylated cyclohexanedimethanol diacrylate, alkoxylated hexanediol diacrylate, alkoxylated neopentyl glycol diacrylate, bis [1- (2-acryloxy)]-p-ethoxyphenyldimethylmethane, bis [1- (3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, 1,2,4-butanetriol trimethacrylate, caprolactone modified neopentyl glycol hydroxypivalate diacrylate, (meth) acrylated monomer and Oligomer copolymerizable mixture, diethylene glycol diacrylate, dipropylene glycol diacrylate, ethoxylated (10) bisphenol A diacrylate Ethoxylated (3) bisphenol A diacrylate, ethoxylated (30) bisphenol A diacrylate, ethoxylated (4) bisphenol A diacrylate, ethylene glycol diacrylate, glycerol diacrylate, neopentyl glycol diacrylate, glycol hydroxypivalate di Acrylate, hydroxypivalaldehyde modified trimethylolpropane diacrylate, polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate, propoxylated neopentyl glycol diacrylate, molecular weight per mole About 200-500 grams of polyethylene glycol bis-acrylate and bis-methacrylate , Tricyclodecane dimethanol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tripropylene glycol diacrylate, tetraethylene glycol diacrylate, pentaerythritol triacrylate, glycerol triacrylate, ethoxylated triacrylate (eg , Ethoxylated (3) trimethylolpropane triacrylate, ethoxylated (6) trimethylolpropane triacrylate, ethoxylated (9) trimethylolpropane triacrylate, ethoxylated (20) trimethylolpropane triacrylate), pentaerythritol triacrylate , Propoxylated triacrylates (eg propoxylated (3) glyceryl triacrylates) Rate, propoxylated (5.5) glyceryl triacrylate, propoxylated (3) trimethylolpropane triacrylate, propoxylated (6) trimethylolpropane triacrylate), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, sorbitol Hexaacrylate, trimethylolpropane triacrylate, tris (hydroxyethyl) isocyanurate trimethacrylate, unsaturated amide (eg, methylene bis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylene bis-acrylamide, diethylenetriamine tris-acrylamide, and β-methacrylamideamidomethacrylate), and combinations thereof; and vinyl compounds (eg, Styrene, diallyl phthalate, divinyl succinate, divinyl adipate, and divinyl phthalate, and combinations thereof); and combinations thereof. Other useful free radical polymerizable compounds include (meth) acrylated oligomers and polymers.

  Suitable (meth) acrylated polymers include, for example, polymers with acrylate and / or methacrylate pendant groups having from 1 to about 50 (meth) acrylate groups per polymer chain. Examples of such polymers include, for example, Sartomer Co. And aromatic acid (meth) acrylate half ester resins such as “SARBOX” (eg, SARBOX 400, 401, 402, 404, and 405) sold by (Exton, Pennsylvania). Other useful reactive polymers curable by free radical chemistry include free radical polymerizable functionalities attached thereto such as those described in US Pat. No. 5,235,015 (Ali et al.). These polymers include hydrocarbyl backbones with peptide pendant groups. Mixtures of two or more monomers, oligomers, and / or reactive polymers can be used as desired. Typical ethylenically unsaturated species include acrylates, aromatic acid (methacrylate) acrylate half-ester resins, and hydrocarbyl backbones and peptide pendant groups that are functionalized with radical polymerization. Polymers.

  A multi-photon photoinitiator system simultaneously absorbs at least two photons of light from a light source and generates free radicals that can initiate free radical polymerization of free radically polymerizable compounds in the photocurable composition. The multi-photon photoinitiator system makes it possible to limit or limit the polymerization to the focal region of the focused beam of light. Such a system is a one-component, two-component system comprising at least one multiphoton photosensitizer, at least one photoinitiator (or electron acceptor) and optionally at least one electron donor. Or a three-component system. Such multi-component systems can provide improved sensitivity and can achieve a light response in a shorter period of time, thereby resulting in movement of one or more components of the sample and / or exposure system. The potential for problems is reduced. The multiphoton photoinitiator system is capable of simultaneously absorbing at least two photons, and optionally has a photochemically effective amount of at least one multiphoton absorbing compound having a two-photon absorption cross-section greater than fluorescein. May be advantageously included.

  In some embodiments, the multi-photon photoinitiator system can be a one-component system that includes a Type I photoinitiator for free radical polymerization. A type I photoinitiator is defined as one that essentially undergoes a single molecule bond cleavage reaction by absorption of light, thereby producing a free radical. Suitable Type I photoinitiators include, for example, benzoin ether (eg, benzoin methyl ether, benzoin ethyl ether, benzoin n-butyl ether), benzyl ketal (eg, IRGACURE 651 from Ciba Specialty Chemicals (Tarrytown, New York)). 2,2-dimethoxy-1,2-diphenylethane-1-one); α-substituted acetophenone derivatives (for example, 2-hydroxy-2-methyl-1-phenyl sold by Ciba Specialty Chemicals as DAROCUR 1173) -1-propanone); and 1-hydroxysilane sold as IRGACURE 184 by Ciba Specialty Chemicals Chlohexyl phenyl ketone; 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one sold as IRGACURE 907 from Ciba Specialty Chemicals Corporation; IRGACURE 36 sold as Ciba Specialty Chemicals Corporation 2-benzyl-2- (dimethylamino) -1- [4- (4-morpholinyl) phenyl] -1-butanone; and acylphosphine oxide (eg, bis (2 sold by IRBACURE 819 from Ciba Specialty Chemicals) , 4,6-trimethylbenzoyl) phenylphosphine oxide, and BASF Corp. (Fl 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide sold as LUCIRIN TPO-L by rham Park, New Jersey), and mono- and bis-acylphosphines (eg IRGACURE 1700, IRGACURE 1800 from Ciba Specialty Chemicals) IRGACURE 1850, IRGACURE 819 IRGACURE 2005, IRGACURE 2010, IRGACURE 2020, and DAROCUR 4265); and oligomeric photoinitiators (eg, ESACU from Galbert, Italy 100 -Geigy ( autertal, IRGACURE 651) and the like sold by Germany). A combination of two or more photoinitiators can also be used. In addition, sensitizers such as 2-isopropylthioxanthone can be used with photoinitiators such as “IRGACURE 369”.

  In some embodiments, the multiphoton photoinitiator system is a two-component system (eg, a combination of an electron donor and a photoinitiator) or a three-component system (eg, an electron donor, a sensitizer, and a photoinitiator). Combination). Multiphoton photosensitizers, electron donors, and photoinitiators (or electron acceptors) useful in two-component and three-component multiphoton photoinitiator systems are described below.

  Multiphoton photosensitizers are known in the art, and exemplary embodiments having relatively large multiphoton absorption cross sections are generally described, for example, in US Pat. No. 6,267,913 (Marder et al.). ing. The photosensitizer can have a two-photon absorption cross-section greater than about 1.5 times that of fluorescein, more than about 2 times that of fluorescein, more than about 3 times that of fluorescein, or even more than about 4 times that of fluorescein. In some embodiments, the photosensitizer is soluble in a free-radically polymerizable compound (eg, when the free-radically polymerizable compound is a liquid) or a free-radically polymerizable compound included in the composition And is compatible with any binder (eg, those described below). One of the sensitizers can be selected in consideration of storage stability. Thus, the choice of a particular photosensitizer may depend to some extent on the particular free radical polymerizable compound utilized (and the choice of electron donor compound and / or photoinitiator).

  Particularly useful multiphoton photosensitizers include rhodamine B (ie, N- [9- (2-carboxyphenyl) -6- (diethylamino) -3H-xanthen-3-ylidene] -N-ethylethaneaminium). Chloride or hexafluoroantimonate) and large multiphotons such as, for example, four types of photosensitizers described by Marder and Perry et al. In International Patent Publication Nos. WO 98/121521 and 99/53242. The thing which exhibits an absorption cross-sectional area is mentioned. The four classes are: (a) a molecule in which two donors are bonded to a conjugated π-electron bridge, (b) a bond to a conjugated π-electron bridge in which two donors are substituted with one or more electron withdrawing groups. (C) a molecule in which two receptors are bonded to a conjugated π-electron bridge, and (d) a bond in which two receptors are substituted with one or more electron-donating groups. Molecules (wherein “bridge” means a molecular fragment that binds two or more chemical groups, and “donor” means an atom or a low ionization potential that can be attached to a conjugated π-electron bridge) It means an atomic group and “acceptor” can be described as an atom or atomic group having a high electron affinity that can be bound to a conjugated π-electron bridge. Other useful photosensitizers are described in US Pat. Nos. 6,100,405, 5,859,251, and 5,770,737 to Reinhardt et al. With large multiphoton absorption cross sections. These cross-sectional areas are determined by methods other than those described above.

  Electron donor compounds useful in the multiphoton photoinitiator system of the photocurable composition are those compounds (other than the photosensitizer itself) that can donate electrons to the electronically excited state of the photosensitizer. Such compounds can optionally be used to increase the multiphoton photosensitivity of the photoinitiator system, thereby reducing the exposure required to effect the photoreaction of the photocurable composition. . The electron donor compound may have an oxidation potential that is greater than zero and less than or equal to that of p-dimethoxybenzene. In some embodiments, the oxidation potential is about 0.3-1 volt relative to a standard saturated calomel electrode ("SCEE").

  The electron donor compound is typically soluble in the photocurable composition, but this is not a requirement and can be selected with some consideration of storage stability (as described above). Suitable electron donors are generally capable of increasing the cure rate or image density of the photocurable composition when exposed to light of the desired wavelength.

  In general, electron donor compounds suitable for use with certain photosensitizers and photoinitiators are three component (eg, described in US Pat. No. 4,859,572 (Farid et al.)). Can be selected by comparing the oxidation potential and the reduction potential.

Suitable electron donor compounds include, for example, amines (triethanolamine, hydrazine, 1,4-diazabicyclo [2.2.2] octane, triphenylamine (and its triphenylphosphine and triphenylarsine analogs), Amino aldehyde, amino silane), amide (including phosphoramide), ether (including thioether), urea (including thiourea), sulfinic acid and its salt, ferrocyanide salt, ascorbic acid and its salt, dithiocarbamic acid And its salts, xanthates, ethylenediaminetetraacetates, (alkyl) _n (aryl) _m borates (n + m = 4) (eg tetraalkylammonium salts), various organometallic compounds such as SnR ₄ compounds (formulas) R is independently alkyl, aralkyl (especially ben Jill), aryl, and alkaryl groups) _{(e.g., n-C 3 H 7 Sn} (CH 3) 3, ( allyl) Sn _{(CH 3) 3,} and (benzyl) Sn _(n-C 3 H ₇ ) Compounds such as ₃ ), ferrocene, and mixtures thereof. The electron donor compound can be unsubstituted or substituted with one or more non-interfering substituents. In some embodiments, suitable electron donor compounds include an electron donor atom (such as a nitrogen atom, an oxygen atom, a phosphorus atom, or a sulfur atom) and a carbon atom that is alpha to the electron donor atom or A removable hydrogen atom bonded to a silicon atom.

Suitable photoinitiators (ie, electron acceptor compounds) for use in the photocurable composition accept electrons from an electronically excited multiphoton photosensitizer, resulting in at least one free radical and A photoinitiator that can be sensitized by the formation of acid. Such photoinitiators include iodonium salts (eg, diaryl iodonium salts), sulfonium salts (eg, optionally substituted with alkyl or alkoxy groups, and optionally bridge adjacent aryl moieties). And triarylsulfonium salts having a 2,2′-oxy group), and combinations thereof. Suitable iodonium salts include those described in US Pat. No. 5,545,676 (Palazzott et al.). Iodonium salts include, for example, simple salts (eg, containing anions such as chloride, bromide, iodide, or benzenesulfonate) or metal complexes (eg, SbF ₆ ⁻ , PF ₆ ⁻ , BF ₄ ⁻ , tetrakis (perfluorophenyl) borane. Acid salt, SbF ₅ OH ⁻ , or AsF ₆ ^— ). If desired, a mixture of iodonium salts can be used.

  The multiphoton photoinitiator system is typically selected to be soluble in the photocurable composition and storage stable (ie, not spontaneously promoting the reaction of the photocurable composition) These are not requirements. Thus, the selection of a particular multiphoton photoinitiator system may depend to some extent on the specific photocurable composition.

  The components of the multiphoton photoinitiator system are present in a photochemically effective amount after removing volatile components such as solvents. Generally, the photocurable composition can be from at least about 5 weight percent (eg, at least about 10 weight percent or at least about 20 weight percent) up to 99.79 weight percent (eg, up to about 95 weight percent or up to about 80 weight percent). Percent) of one or more free-radically polymerizable compounds; from at least about 0.01 weight percent (eg, at least about 0.1 weight percent or at least about 0.2 weight percent) to up to 10 weight percent (eg, , Up to about 5 weight percent or up to about 2 weight percent) multiphoton photoinitiator systems, although other amounts can be used. For example, in two-component and three-component multiphoton photoinitiator systems, up to about 10 weight percent (eg, up to about 5 weight percent) of one or more based on the total solid weight of the photocurable composition An electron donor compound (eg, at least about 0.1 weight percent or about 0.1 to about 5 weight percent); up to 10 weight percent (eg, up to about 5 weight percent) photosensitizer (eg, at least about 0 .001 weight percent to 1 weight percent); and about 0.1 weight percent to about 10 weight percent of one or more electron donor compounds (eg, about 0.1 to about 5 weight percent), but others The amount of can also be used. In embodiments where an organic free radical inhibitor is present, an effective amount thereof may be present. In some embodiments, based on the weight of the photocurable composition, the organic free radical inhibitor is about 0.01 to about 2 weight percent, about 0.01 to about 0.75 weight percent, or about 0.0. It is present in an amount of 1 to about 0.5 weight percent, although other amounts can be used.

  Further details regarding two-component and three-component photoinitiator systems can be found in US Pat. No. 8,004,767 B2 (DeVoe et al.).

  The photocurable composition may further comprise optional components such as one or more polymer binders, stabilizers, fragrances, fillers, thixotropic agents, colorants, free radical thermal initiators, monohydroxys. And polyhydroxy compounds, plasticizers, reinforcing agents, fillers, abrasive particles, stabilizers, light stabilizers, antioxidants, fluidizers, thickeners, matting agents, colorants, swelling agents, antifungal agents , Fungicides, surfactants, fillers such as glass and ceramic beads, and reinforcing materials such as organic and inorganic woven and nonwoven webs.

  In some embodiments, the photocurable composition includes a polymeric binder, for example, to control viscosity and provide film-forming properties. Such polymeric binders can generally be selected to be compatible with free radically polymerizable compounds. For example, a polymer binder that is compatible with the same solvent used for the free radical polymerizable compound and does not contain a functional group that can adversely affect the reaction pathway of the free radical polymerizable compound, Can be used. The binder may be of a molecular weight suitable to achieve the desired film formability and solution rheology (eg, about 5,000 to 1,000,000 daltons, about 10,000 to 500,000 daltons, or about 15 , 20,000-250,000 dalton molecular weight). Suitable polymeric binders include, for example, polystyrene, poly (methyl methacrylate), poly (styrene) -co- (acrylonitrile), and cellulose acetate butyrate.

  In some embodiments, the photocurable composition comprises about 30 weight percent poly (methyl methacrylate) (120,000 grams / mole), about 35 weight percent ethoxylated trimethylolpropane triacrylate (Sartomer Co., Ltd.). Inc. (sold as SR-9008 from Exton, Pennsylvania), and about 35 weight percent tris- (2-hydroxyethyl) isocyanurate triacrylate.

  The photocurable composition is a method known in the art under appropriate “safe light” conditions, for example, to prevent undesired single photon initiated photopolymerization that can cause premature curing of the photocurable composition. Can be formed by combining the above components by mixing together using, for example, stirring or shaking. The components of the photocurable composition can be mixed using any order and method of mixing (optionally with stirring or shaking) under “safe light” conditions, but in some cases Is advantageously added (in terms of shelf life and thermal stability) at the end (and after a heating step optionally used to promote dissolution of the other components). A solvent can be used as desired, provided that the solvent is chosen so that it does not react appreciably with the components of the composition. Suitable solvents include, for example, acetone, dichloromethane, cyclopentanone, and acetonitrile. The free-radically polymerizable compound can optionally serve as a solvent for other components.

  The photocurable composition may be present in any form such as, for example, a liquid or a solid. Prior to light exposure, the photocurable composition is optionally coated onto the substrate using any of a variety of coating methods known to those skilled in the art, including, for example, knife coating and spin coating. be able to. The substrate can be selected from a variety of films, sheets, and other surface materials (including silicon wafers and glass plates) depending on the particular application and the method of exposure utilized. Prior to coating the substrate with the multiphoton curable photocurable composition, the substrate may be primed with a suitable compound, such as a compound containing a silane group and a functional group similar to the photocurable composition. Suitable primers include, for example, 3-trimethoxysilylpropyl methacrylate. Useful substrates can advantageously be sufficiently flat so that a layer of photocurable composition having a uniform thickness can be prepared. For applications where coating is less desirable, the photocurable composition can be exposed in bulk form.

  The multi-photon photocuring practiced herein is a photocurable composition that progresses to the extent that insolubilization of a volume region of the photocurable composition occurs (eg, thereby producing one or more voxels). Free radical polymerization of free radical polymerizable components in the product is included. Typically this is caused by the formation of a crosslinked polymer network that occurs when a multifunctional free radical polymerizable monomer is included in the photocurable composition, although other factors may also affect it. . It should be noted that insolubilization typically depends on the degree of polymerization / crosslinking, so that the photocurable composition may not become insoluble (eg, in a cured state) even if some degree of polymerization occurs. Further insolubilization may also depend on the specific choice of development conditions (eg, rinsing solvent and / or temperature).

  Generally speaking, two conditions must be met for multiphoton photocuring by exposure to occur. The first condition is that the light (eg, high intensity laser light) must have sufficient intensity to allow multiphoton absorption. Additional benefits may be obtained if the light is coherent (eg, as in the case of laser light). As a first approximation, the probability of nonlinear multiphoton absorption increases exponentially with increasing number of absorbed photons. Thus, for practical reasons, multiphoton absorption is typically practiced as two-photon absorption, particularly in condensed phase materials (eg, solids or liquids).

  In a multiphoton photocuring process, multiphoton absorption of light by a multiphoton initiating system causes a reaction or decomposition that generates an initiating chemical species (eg, a free radical) that cures an area of the photocurable composition. (For example, by polymerization with free radicals). Thus, the second condition is that a sufficient number of starting species must be generated to cause sufficient curing of the photocurable composition such that the development material does not remove the desired material. It is. This second condition is related to the amount of light received (eg reflected by the writing speed of the light beam).

  One exemplary type of system that can be used is shown in FIG. Referring to FIG. 1, the fabrication system 10 includes a light source 12, an optical system 14 that includes a final optical element 15 (optionally including a galvano mirror and a telescope that controls light spread), and a movable stage 16. Stage 16 can move in one, two, or more, typically three dimensions. The light rays 26 originating from the light source 12 pass through the optical system 14 and leave through the final optical element 15 and concentrate it at a point P in the layer 20, thereby creating a three-dimensional spatial distribution of the light intensity within the composition. And at least a portion of the photocurable composition 24 in the vicinity of point P is made more or less soluble in the light beam 26 in at least one solvent than immediately prior to exposure. The focal point P can be scanned by moving the stage 16 or directing the beam 26 in combination with the movement of one or more elements of the optical system 14 (eg, moving the laser beam using a galvo-mirror). Alternatively, the shape can be changed to a three-dimensional pattern corresponding to the desired shape. For example, the stage 16 can move in the x and y dimensions, and the final optical element 15 can move in the z dimension, thereby controlling the position of the point P. The reacted or partially reacted part of the photocurable composition 24 forms a three-dimensional structure having a desired shape.

  The substrate 18 mounted on the stage 16 has a layer 20 of a multiphoton photocurable composition 24 disposed thereon. The light beam 26 originating from the light source 12 passes through the optical system 14, leaves through the final optical element 15, and concentrates it at a point P in the layer 20. Thereby, the three-dimensional spatial distribution of light intensity is controlled in the multiphoton photocurable composition 24, and at least a part of the multiphoton photocurable composition 24 near the point P is cured.

  Moving the stage 16 in combination with the movement of one or more elements of the optical system 14 or directing the light beam 26 (e.g., using a galvo-mirror and a telescope to move the laser beam), the focus P The shape can be scanned or changed to a three-dimensional pattern corresponding to the desired shape. Next, the cured or partially cured portion of the resulting multiphoton photoreactive composition 24 forms a three-dimensional structure of the desired shape. If it is desired to form a three-dimensional structure anchored to the substrate after development, the focal point P is fixed at the interface between layer 20 and substrate 18 so that these voxels are the bottom surface of the structure. For example, in a single pass, the surface contour of one or more light extraction structures (corresponding to about one volume pixel or voxel thickness) can be exposed or imaged, and the development can form the surface of the structure.

  Surface contour exposure or imaging can be performed by scanning at least the periphery of a planar slice of the desired three-dimensional structure, and then scanning a plurality of typically parallel planar slices to finish the structure. . The slice thickness can be controlled in conjunction with the appropriate energy dose applied, thereby achieving a sufficiently low surface roughness and providing a high quality structure. For example, a smaller slice thickness is desirable in areas of larger structural taper and can help achieve high structural fidelity, but a larger slice thickness is utilized and useful in areas of smaller structural taper Can help maintain a good production time. Thus, surface roughness below the slice thickness (eg, less than about 1/2 of the slice thickness, or even less than about 1/4 of the slice thickness) depends on the production rate (ie, throughput or unit time). This can be achieved without sacrificing the number of structures produced per hit.

  When coating the multiphoton photoreactive composition 24 on a substrate that exhibits some degree of non-planarity at a dimensional scale equal to or greater than the voxel height, it is necessary to avoid optically or physically defective structures. It may be desirable to compensate with flatness. This locates the interface between the substrate (eg, using a confocal interface locator system) and the portion of the multiphoton photoreactive composition 24 that is to be exposed, and then rays 26 are applied to that interface. Can be achieved by adjusting the position of the optical system 14 to properly focus. A representative example of such a procedure is detailed in US Pat. No. 7,893,410 B2 (Sykora et al.). This procedure can be followed for at least one structure for every 20 structures in the array (eg, at least one for every 10 structures in the array, or each structure).

The light source 12 can be any light source (eg, a laser) that provides sufficient intensity to provide a multiphoton absorption effect at a wavelength suitable for the multiphoton photoinitiator system included in the photocurable composition. ). Such wavelengths can range, for example, from about 300 to about 1500 nm, from about 400 to about 1100 nm, from about 600 to about 900 nm, or from about 750 to about 850 nm (including values at both ends). Typically, the optical fluence (eg, pulsed laser peak intensity) is greater than about 10 ⁶ W / cm ² . The upper limit of light fluence is generally defined by the ablation threshold of the photocurable composition. Suitable representative light sources include high power lamps and lasers. In general, light is not at a wavelength that is absorbed directly (eg, by one-photon absorption) by the photocurable composition, but multiphoton (eg, two-photon) absorption is multiphoton light at half the wavelength (λ / 2). The appropriate wavelength (λ) should correspond to the main absorption by the initiator system. Such wavelengths can typically range from about 300 to about 1500 nm (eg, from about 400 to about 1100 nm, from about 600 to about 900 nm, or from about 750 to about 850 nm, including all ranges). Typically, the optical fluence (eg, peak intensity of a pulsed laser) is greater than about 10 ⁶ watts per square centimeter (W / cm ² ). The upper limit of light fluence is generally defined by the ablation threshold of the photocurable composition.

Suitable light sources include, for example, ultrafast lasers such as picosecond lasers and femtosecond lasers. For example, as a suitable femtosecond laser, a near-infrared titanium sapphire oscillator (eg, Coherent (Santa Clara, California) excited by an argon ion laser (eg, sold by Coherent under the trade designation “INNOVA”). (Trade name “MIRA OPTIMA 900-F”). This laser operates at 76 MHz, has a pulse width of less than 200 femtoseconds, is tunable between 700-980 nm, and has an average power of up to 1.4 watts. Another useful laser is sold by Spectra-Physics (Mountain View, California) under the trade designation “MAI TAI”, which is tunable within the range of 750-850 nanometers and has a repetition frequency of 80 megahertz. A pulse width of about 100 femtoseconds ( ^10-13 seconds) and an average power of up to 1 watt.

  Other suitable lasers include Q-switched Nd: YAG lasers (eg, those sold by Spectra-Physics under the trade name “QUANTA-RAY PRO”), visible wavelength dye lasers (eg, QUANTA-RAY PRO Q -Switched Nd: pumped by a YAG laser, sold under the trade name "SIRAH" by Spectra-Physics, and Q-switched diode pumped laser (for example, sold by Spectra-Physics under the trade name "FCBAR") Are).

Additional light sources include near infrared pulsed lasers having a pulse length of less than about 10 ⁻⁸ seconds (eg, less than about 10 ⁻⁹ seconds, or even less than about 10 ⁻¹¹ seconds). Other pulse lengths can be used as long as the above peak intensity and ablation threshold criteria are met. For example, the pulsed light has a pulse frequency from about 1 kilohertz to about 50 megahertz (MHz) or even higher. A continuous wave laser can also be used.

  The optical system 14 includes, for example, a refractive optical element (for example, a lens or a microlens array), a reflective optical element (for example, a retroreflector or a focusing mirror), a diffractive optical element (for example, a diffraction grating, a phase mask, and a hologram), Polarization optical elements (eg, linear polarizers, circular polarizers, and wave plates), dispersive optical elements (eg, prisms and diffraction gratings), diffusion plates, Pockels cells, waveguides, etc. can be included. Such optical elements are useful for focusing, beam delivery, beam / mode shaping, pulse shaping, and pulse timing. In general, optical elements can be used in combination, but other suitable combinations will be recognized by those skilled in the art.

  The final optical element 15 may include, for example, one or more refractive, reflective and / or diffractive optical elements. In certain embodiments, for example, an objective lens, such as used in microscopy, is readily available from suppliers such as, for example, Carl Zeiss, North America (Thornwood, New York) and used as the final optical element 15. Can do. For example, the fabrication system 10 includes a scanning confocal microscope (e.g., Bio-) equipped with an objective lens having a NA of 0.75 (e.g., sold under the trade name "20X FLUAR" by Carl Zeiss, North America). Rad Laboratories (available from Hercules, Calif.) Under the trade designation “MRC600”). The numerical aperture of the final optical element 15 can have any value in the range of 0.65 to 1.46 (including values at both ends). Useful aerial objectives typically have a numerical aperture in the range of 0.65 to about 0.95. Useful immersion objectives (eg, oil immersion objectives) typically have numerical apertures in the range of greater than about 1.0 to 1.46.

  In order to provide highly focused light, it may often be desirable to use an optical system with a relatively large numerical aperture. However, any combination of optical elements that provides the desired intensity profile (and its spatial arrangement) can be used.

In general, the exposure time is the type of exposure system (and numerical aperture, shape of light intensity spatial distribution, peak light intensity during laser pulse) used to cause the reaction of free radically polymerizable compounds within the photocurable composition. Dependent variables such as intensity (higher intensity and shorter pulse duration, roughly corresponding to the intensity of the peak light), as well as the nature of the photocurable composition. In general, when all other conditions are equal, the higher the peak light intensity in the focal region, the shorter the exposure time. In general, one-dimensional imaging or “writing” rates are about 10 ⁻⁸ to 10 ⁻¹⁵ seconds (eg, about 10 ⁻¹¹ to 10 ⁻¹⁴ seconds) and about 10 ² to 10 ⁹ pulses / second (eg, about 10 ³ to A laser pulse duration of 10 ⁸ pulses / second), and may be from about 0.5 to 100,000 micrometers / second.

  Unless otherwise stated, multiple light rays can be used that may have different cross-sectional light intensity profiles and / or temporal profiles. This light beam can be emitted from one or more light sources (eg, lasers). Using the same light source for multiple rays may simplify the multi-photon photocuring process and possibly simplify system design and implementation.

  Due to multiphoton absorption, exposure to light beam 26 induces a reaction in the photocurable composition and produces one or more volume regions of cured material, including free radical polymerized material. Next, the pattern produced by the cured material and the uncured material can be realized by conventional development methods, for example by removing the uncured areas. Optionally, after only the surface features of the desired structure have been exposed, they are typically subjected to solvent development and non-imaging exposure using actinic radiation (eg, light that causes curing by a one-photon absorption process), optionally An additional curing effect can be provided to the remaining uncured photocurable composition. Complex three-dimensional structures and structure arrays can be prepared in this way.

  In order to successfully solvent develop the exposed photocurable composition and obtain the resulting structure, a threshold dose of light (ie, a threshold amount) in the volume region (voxel) of the photocurable composition where curing is desired. Is typically necessary. Thus, the light dose typically is such that the volume region where curing is desired receives at least a threshold level (eg, up to 10 times the threshold level) and in the volume region where negative contrast is utilized. The strength is typically selected to be greater. This threshold dose is typically process specific, eg, wavelength, pulse frequency, light intensity, specific photocurable composition, specific structure made, or process used for solvent development. Can depend on variables such as Thus, each set of process parameters typically involves a unique threshold dose.

  Through multiphoton absorption, light beam 26 induces a free radical polymerization reaction in the photocurable composition, thereby forming a volume region of material having a solubility characteristic that is different from the unexposed region of the photocurable composition. . The resulting different solubility patterns can be materialized by conventional development processes, for example, by removing either exposed or unexposed areas. The exposed photocurable composition can be, for example, by placing the exposed photocurable composition in a solvent, dissolving areas of higher solvent solubility, rinsing with solvent, evaporating, oxygen plasma etching, or It can be developed by other known methods and combinations thereof. Non-limiting examples of solvents that can be used to develop the exposed photocurable composition include, for example, water (eg, having a pH in the range of 1-12), water and organic solvents. Examples include aqueous solvents such as compatible mixtures with (for example, methanol, ethanol, propanol, acetone, acetonitrile, dimethylformamide, N-methylpyrrolidone, mixtures thereof, and the like), and organic solvents. Representative examples of useful organic solvents include alcohols (eg, methanol, ethanol, propanol), ketones (eg, acetone, cyclopentanone, methyl ethyl ketone), aromatics (eg, toluene), organic halogen compounds (eg, Methylene chloride, chloroform), nitriles (eg acetonitrile), esters (eg ethyl acetate, propylene glycol methyl ether acetate), ethers (eg diethyl ether, tetrahydrofuran), amides (eg N-methylpyrrolidone), and these Combinations are listed.

  Suitable photocurable compositions for practicing the present disclosure exhibit a negative contrast under certain process conditions. For example, if exposure is performed above the threshold volume necessary to obtain multiphoton absorption, the photocurable composition may exhibit increased cure and then decrease cure as the light dose increases. . This can be seen by plotting the vertical voxel dimensions (eg, obtained after solvent development) against the reciprocal of writing speed for a fixed multiphoton cure condition, for example as shown in FIG. Here, the writing speed reflects the moving speed of the laser beam across the body containing the photocurable composition. FIG. 2 shows an increase in vertical voxel dimension in region 210 with a decrease in writing speed (ie, an increase in the reciprocal of writing speed corresponding to an increase in dose), which is a problem for many multiphoton processes. It is common. However, if the write speed is further decreased (ie, the reciprocal of the write speed is further increased), the maximum level 220 is reached. As the writing speed decreases and enters region 230, the dose further increases, resulting in a decrease in vertical voxel size. This decrease in cure with increasing dose is an example of negative contrast (ie, a contrast curve with a negative slope region). This negative contrast phenomenon can be advantageously utilized by the present disclosure to provide imaging capabilities below the diffraction limit normally associated with imaging with light.

  There is a non-uniform spatial property of light impinging on the photocurable composition to create structures formed from voxels with dimensions below the diffraction limit of the light used, using negative contrast phenomena There is a need to. For example, a light beam formed by combining two separate light beams can have higher intensity and / or dose in some parts than other parts, for example, as described herein. . Under conditions where negative contrast is observed, photocuring is inhibited in the region of maximum intensity / dose, while adjacent regions exhibit a greater degree of photocuring.

  Without being bound by theory, the inventors believe that negative imaging has found that free radicals are excessively produced, leading to premature termination of free radical polymerization and a reduced degree of cure.

Thus, a single tightly focused beam with non-uniform beam intensity creates a structure and component with sub-micrometer resolution (eg, as described hereinabove). Can be used for In one embodiment, this ray has the strongest intensity in the outer region of the periphery and has a very low cross-section in the middle of the ray. For example, the ray may have a ray cross-sectional profile that includes an inner region with a relatively low light intensity surrounded by an outer region with a relatively high light intensity, where the inner and outer regions are at the same time. Has a dynamic profile (which can be continuous or pulsed). This can be done, for example, by Gauss-Laguerre mode (eg TEM ₀₁ ^* (doughnut shape as shown in FIG. 3) or TEM ₁₀ (“cat eye” shape as shown in FIG. 4)) or by known methods It can be achieved by using a Gaussian Hermite mode that can be formed with a suitable phase mask. When using TEM ₀₁ ^* Gauss-Laguerre mode light, curing is caused by light in the inner region (it is recognized that at least some light is almost always present in the inner region), whereas a photocurable composition The light in the outer region focused on the object is of sufficient intensity and dose that inhibits the curing of the photocurable composition. As a result, curing preferentially occurs in the inner region and decreases as it approaches the outer region, resulting in a smaller cured volume (voxel) that can be obtained by conventional single light methods. In some embodiments, this may result in a single shape formed at the center of the ray cross section, but in other embodiments, a central point and an outer ring that is spaced from that point. It can produce an ox eye shape. The use of TEM ₁₀ Gauss-Laguerre mode rays can similarly result in the formation of sub-micrometer structures such as rings and tubes. This method advantageously simplifies the optical steering requirements that may exist in the case of multiple high-intensity rays, with very small micrometer dimensions or at a slower writing speed than other conventional multi-photon methods. Sub-micrometer sized structures can be formed and can result in improved process control.

While the foregoing section describes the use of a laser beam that includes an inner region of relatively low light intensity surrounded by an outer region of relatively high light intensity, in some methods of the present disclosure, In the case of wiring lines, for example, it may be advantageous to use other laser beam modes. Examples of laser modes that can be used as such include TEM ₀₁ , TEM ₀₂ , TEM ₀₃ , and TEM ₁₁ .

  In other applications of finding possible causes of negative contrast, the present disclosure further achieves negative contrast during multiphoton photocuring of a substantially anoxic photoreactive system. The advantages and methods of using a negative contrast photocurable composition for microstructure fabrication are described herein above.

  It is well known that oxygen inhibits free radical polymerization, alone or optionally with certain inhibitors (eg, hydroquinone monomethyl ether (MEHQ), etc.) that are effective only in the presence of molecular oxygen. In this embodiment, free radical polymerization inhibitors other than oxygen are included in the photocurable composition to provide this benefit in place of oxygen. Of particular note in this embodiment, negative contrast imaging can be achieved using organic free radical polymerization inhibitors at concentrations far exceeding those that would normally be included in free radical polymerizable compositions. For example, in this embodiment, the concentration of the organic free radical polymerization inhibitor is 0.01 to 2 weight percent (eg, about 0.1 to 0.75 weight percent) based on the total weight of the photocurable composition. A range of amounts can be included in the photocurable composition, although other amounts can be used.

  Advantageously, in this embodiment, the substantial absence of molecular oxygen makes it possible to adjust the sensitivity of the photocurable composition by adjusting the concentration of the organic free radical polymerization inhibitor. Certain organic free radical polymerization inhibitors, such as, for example, phenol type antioxidants (eg, hydroquinone, 4-methoxyphenol (MEHQ), and 2,6-di-tert-butyl-4-methylphenol) are generally These are typically of little or no use in this embodiment because they are effective only in inhibiting free radical polymerization only in the presence of molecular oxygen.

  Useful organic free radical polymerization inhibitors that can inhibit free radical polymerization in the absence of oxygen include, for example, phenothiazine and amine oxide radicals (eg, 2,2,6,6-tetramethylpiperidinooxy (ie, TEMPO), 4-hydroxy-TEMPO; 4-acetamido-TEMPO, 4-amino-TEMPO, 4-cyano-TEMPO, 4- (2-iodoacetamido) -TEMPO, 4-oxo-TEMPO, 4-methoxy-TEMPO, 4-phosphonooxy-TEMPO hydrate, poly (ethylene glycol) -bis-TEMPO, 4-methanesulfonyloxy-TEMPO, 4-methacryloyloxy-TEMPO, bis (1-oxyl-2,2,6,6-tetramethyl Piperidin-4-yl) sebacate); -Triphenyl verdazyl radical, galvinoxyl radical; 1,3-bisdiphenylene-2-phenylallyl radical (Kersch radical); and N-nitrosophenylhydroxylamine salts (eg Q-1300 and Q-1301 from Wako Chemical) Are sold as).

  In yet other applications of this discovery of possible causes of negative imaging, the present disclosure further includes free radical polymerizable compounds and type I photoinitiators (both previously described herein), and at least one of A negative contrast phenomenon is achieved during multiphoton curing of photoreactive systems, including free radical polymerization inhibitors. In this embodiment, free-radically polymerizable methacrylates, acrylates, and similar compounds can be used.

  Type I photoinitiators have the advantage of being readily available from relatively low cost commercial sources compared to other known multiphoton photoinitiator systems. However, until now, no negative contrast has been observed during multiphoton curing of photocurable compositions. Thus, it has now been discovered that negative imaging can be observed in free radical curable systems containing free radical polymerizable compounds (eg, acrylates or methacrylates). In some embodiments, the free radical curable system comprising methacrylate is less than 1 weight percent of other free radical polymerizable compounds, such as acrylates and acrylamides, based on the total weight of the photocurable composition, or Furthermore, it contains less than 0.1 weight percent. In some cases, the photocurable composition may be free of free radical polymerizable acrylate and acrylamide compounds. The advantages and methods of multiphoton curing of photocurable compositions under negative contrast conditions, for example in the production of microstructures, have been described previously herein.

  Selected embodiments of the present disclosure are set forth in detail below.

Selected Embodiments of the Present Disclosure In a first embodiment, the present disclosure includes the following steps:
a) providing a light beam, the light beam having a light beam cross-sectional profile comprising an inner region of relatively low light intensity surrounded by an outer region of relatively high light intensity, wherein Wherein the inner region and the outer region have the same temporal profile; and
b) providing a photocurable composition, the photocurable composition comprising a free radical polymerizable compound, a free radical polymerization inhibitor, and a multiphoton photoinitiator system; ,
c) By exposing at least a portion of the photocurable composition to light, multiphoton absorption by a multiphoton photoinitiator system of a portion of the light initiates free radical polymerization on at least a portion of the free radical polymerizable compound. Wherein irradiating the photocurable composition with at least a portion of the inner region of the light beam causes a portion of the photocurable composition to cure to at least a threshold level for development. And irradiating the photocurable composition with at least a portion of the outer region adjacent to the inner region of the light beam, the photocurable composition does not cure to at least a threshold level for development. A method comprising the steps of:

  In a second embodiment, the present disclosure provides a method according to the first embodiment, wherein the photocurable composition further comprises an organic polymer, wherein the photocurable composition is substantially non-flowable. is there.

  In a third embodiment, the present disclosure provides a method according to the first or second embodiment, wherein the outer region of the beam cross-sectional profile is substantially annular.

  In a fourth embodiment, the present disclosure provides a method according to any one of the first to third embodiments, wherein the light beam comprises Gauss-Laguerre mode laser light.

  In a fifth embodiment, the present disclosure provides a method according to any one of the first to fourth embodiments, wherein the photocurable composition forms a layer, the layer on the substrate. Placed in.

  In a sixth embodiment, the present disclosure provides a method according to any one of the first to fifth embodiments, wherein step c) is repeated a plurality of times, and in each iteration, the light beam is predetermined The various positions in the photocurable composition are focused according to the pattern.

  In a seventh embodiment, the present disclosure provides a method according to the sixth embodiment, wherein the predetermined pattern includes a predetermined pattern variation in each of three dimensions.

  In an eighth embodiment, the present disclosure provides a method according to any one of the first to seventh embodiments, wherein the photocurable composition cured in step c) to at least a threshold level for development. Further developing at least a portion.

  In a ninth embodiment, the present disclosure provides the method according to any one of the first to eighth embodiments, wherein the free radical polymerization inhibitor is a free radical polymerization inhibitor other than molecular oxygen. Including.

  In a tenth embodiment, the present disclosure provides a method according to any one of the first to ninth embodiments, wherein the free-radically polymerizable compound comprises at least two acryloyl groups.

In an eleventh embodiment, the present disclosure includes the following steps:
a) providing at least one light beam;
b) a step of providing a photocurable composition, the photocurable composition comprising a free radical polymerizable compound, a free radical polymerization inhibitor other than molecular oxygen, a multiphoton photoinitiator system, The free radical polymerization inhibitor is effective in the absence of oxygen, and
c) at least a portion of the photocurable composition is at least partially cured by exposing it to at least one light beam, whereby the multiphoton absorption by the multiphoton photoinitiator system of a portion of the light is free radical Initiating free radical polymerization of the polymerizable compound and thereby reducing the degree of curing of at least a portion of the photocurable composition exposed to the light due to the stepwise increase in exposure with the light, the photocurable composition The article provides a method comprising the step of substantially free of molecular oxygen before the photocurable composition is exposed to the light.

  In a twelfth embodiment, the present disclosure provides a method according to the eleventh embodiment, wherein the photocurable composition is about 0.1 to about 0 based on the total weight of the photocurable composition. . 5 weight percent free radical polymerization inhibitor.

  In a thirteenth embodiment, the present disclosure provides a method according to the eleventh or twelfth, wherein the free radical polymerizable compound comprises at least two methacryloyl groups, and the photocurable composition substantially comprises an acrylate. Not included.

  In a fourteenth embodiment, the present disclosure provides a method according to any one of the eleventh to thirteenth embodiments, wherein the photocurable composition further comprises an organic polymer and substantially It is non-fluid.

  In a fifteenth embodiment, the present disclosure provides a method according to any one of the eleventh to fourteenth embodiments, wherein the photocurable composition forms a layer, the layer on the substrate. Placed in.

  In a sixteenth embodiment, the present disclosure provides a method according to any one of the first to fifteenth embodiments, wherein step c) is repeated a plurality of times, and in each iteration, the light beam is predetermined The various positions in the photocurable composition are focused according to the pattern.

  In a seventeenth embodiment, the present disclosure provides a method according to any one of the first to sixteenth embodiments, wherein the predetermined pattern includes a predetermined pattern variation in each of three dimensions. .

  In an eighteenth embodiment, the present disclosure provides a method according to any one of the eleventh to seventeenth embodiments, wherein a photocurable composition cured to at least a threshold level for development in step c). Further developing at least a portion.

In a nineteenth embodiment, the present disclosure includes the following steps:
a) providing a light beam;
b) providing a photocurable composition, the photocurable composition comprising:
A compound capable of free radical polymerization;
A type I photoinitiator;
A process comprising a free radical polymerization inhibitor;
c) a compound capable of at least partially curing at least a portion of the photocurable composition by exposure to light, whereby multiphoton absorption of a portion of the light by a Type I photoinitiator is free radically polymerizable. Initiating free radical polymerization of the light, and thereby reducing the degree of curing of at least a portion of the photocurable composition exposed to the light by stepwise increasing the exposure with the light. To do.

  In a twentieth embodiment, the present disclosure provides a method according to the nineteenth embodiment, and developing at least a portion of the photocurable composition cured in step c) to at least a threshold level for development. In addition.

  In a twenty-first embodiment, the present disclosure provides a method according to the nineteenth or twentieth embodiment, wherein the free radical polymerizable compound is a free radical polymerizable acrylate or free radical polymerizable methacrylate. Including at least one.

  In a twenty-second embodiment, the present disclosure provides a method according to the twenty-first embodiment, wherein the free radical polymerizable compound comprises a free radical polymerizable methacrylate.

  In a twenty-third embodiment, the present disclosure provides a method according to any one of the nineteenth to twenty-second embodiments, wherein the Type I photoinitiator is a substituted or unsubstituted benzoin ether, benzyl It is selected from the group consisting of ketal, α, α-dialkoxyacetophenone, α-hydroxyalkylphenone, α-dialkylaminoalkylphenone, acylphosphine oxide, acylphosphine, substituted derivatives thereof, and combinations thereof.

  In a twenty-fourth embodiment, the present disclosure provides a method according to any one of the nineteenth to twenty-third embodiments, wherein the type I photoinitiator is 2-benzyl-2- (dimethylamino) Contains -4'-morpholinobyllophenone.

  In a twenty-fifth embodiment, the present disclosure provides a method according to any one of the nineteenth to twenty-fourth embodiments, wherein the photocurable composition further comprises an organic polymer and substantially It is non-fluid.

  In a twenty-sixth embodiment, the present disclosure provides a method according to a twenty-fifth embodiment, wherein the photocurable composition forms a layer, and the layer is disposed on a substrate.

  In a twenty-seventh embodiment, the present disclosure provides a method according to the twenty-sixth embodiment, wherein step c) is repeated a plurality of times, each time the light beam is a photocurable composition according to a predetermined pattern. Focus on various locations within the object.

  In a twenty-eighth embodiment, this disclosure provides a method according to a twenty-seventh embodiment, wherein the predetermined pattern includes a predetermined pattern variation in each of three dimensions.

  The following non-limiting examples further illustrate the objects and advantages of the present disclosure, but the specific materials and amounts thereof described in these examples, as well as other conditions and details, unduly limit the present disclosure. It should not be interpreted as a thing.

  Unless otherwise indicated, all parts, ratios (%), ratios, etc. in the examples and the rest of the specification are by weight.

Materials PMMA refers to poly (methyl methacrylate) (MW = 120,000 grams / mole) obtained from Aldrich Chemical Company (Milwaukee, Wisconsin).

  SR 350 trimethylolpropane trimethacrylate, containing 55-75 ppm hydroquinone and about 6 ppm MEHQ inhibitor, was obtained from Sartomer USA, LLC (Exton, Pennsylvania).

  SR 368 tris (2-hydroxyethyl) isocyanurate triacrylate contained 75-125 ppm MEHQ inhibitor and was obtained from Sartomer USA.

  SR 9008 trifunctional acrylate monomer contained 150-325 ppm of MEHQ inhibitor and was obtained from Sartomer USA.

  SR 9009 trifunctional methacrylate monomer contained 160-220 ppm MEHQ inhibitor and was obtained from Sartomer USA.

  IRGACURE 369 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 was obtained from Ciba Specialty Chemicals (Tarrytown, New York).

  KL68 refers to a photosensitizer having the structure I shown below, synthesized according to the description of US Pat. No. 7,265,161 (Leatherdale et al.).

  PTA refers to the free radical polymerization inhibitor phenothiazine.

  MEHQ refers to 4-methoxyphenol, a free radical polymerization inhibitor, obtained from Alfa-Aesar (Ward Hill, Massachusetts).

  TEMPO refers to the free radical polymerization inhibitor 2,2,6,6-tetramethylpiperidinooxy obtained from Sigma-Aldrich (Milwaukee, Wisconsin).

General method for preparing acrylate and methacrylate photoresists coated on a wafer:
An acrylate stock solution is prepared by mixing 30 parts by weight PMMA, 35 parts by weight SR 9008 trifunctional acrylate monomer, and 35 parts by weight SR 368 alkoxylated trifunctional acrylate monomer in cyclopentanone. It was. The resulting solution was 55 weight percent solids in cyclopentanone.

  The methacrylate stock solution is prepared in the same manner as the acrylate stock solution, but instead includes 30 parts by weight PMMA, 35 parts by weight SR 9009 trifunctional methacrylate monomer, and 35 parts by weight SR 350 trimethylolpropane trimethacrylate. It was. The resulting solution was 55 weight percent solids in cyclopentanone.

  Acrylate and methacrylate photoresist solutions were prepared by adding the desired amounts of photoinitiator, photosensitizer, and inhibitor to each of the acrylate and methacrylate stock solutions prepared above. The amounts of photoinitiator, photosensitizer, and inhibitor added to prepare the acrylate and methacrylate photoresist solutions used in Examples 1-10 are listed below. The desired amount of photoinitiator and / or inhibitor was first dissolved in a minimum amount of cyclopentanone and then added to the acrylate or methacrylate stock solution.

  After stirring, the photoresist solution was filtered through a 0.7 micrometer filter and coated on a silicon wafer by spin coating. The resulting photoresist coating was 5-15 micrometers thick.

General methods for measuring writing speed threshold and voxel height:
A simple two-photon writing system was used to examine the writing speed threshold and voxel height. This system is designed to cover top features over a small area (about 0.1 mm ² ), a femtosecond fiber laser (model F) with a central wavelength of 807 nanometers (nm) and a pulse width of 112 femtoseconds (fs) -100, sold by IMRA America, Inc. (available from Ann Arbor, Michigan)) with computer-aided design (CAD) according to laser beam power control, aerial objective lens (40x, numerical aperture 0.95), and writing parameters Equipped with electromagnetic shutter. Samples were mounted on a piezosystem jena TRITOR-400 (piezosystem jena, Jena, Germany) on a computer-driven nanoconfiguration X, Y, Z stage (obtained from Newport Corporation, Santa Clara, Calif.). An Ocean Optics USB-2000 spectrometer (obtained from Ocean Optics, Inc. (Dunedin, Florida)) was used in a confocal interface detection system to accurately and precisely measure the location of the substrate-photoresist interface. This system was capable of scanning speeds of about 1 to 300 micrometers per second.

For each of the photoresist films in the examples below, using the system described above, a different set of two-dimensional 15-line array structures are written at a rate in the range of about 1 to 300 micrometers per second, as shown in FIG. It is. In a given set, each of the 15 lines was written at the same speed, but the Z position was different, where Z _o is the Z position at which the peak of the laser beam reflected at the interface was detected by the fiber spectrum detector. there were. Z _o typically occurred at Z = 179 or 181 micrometers.

  The two-dimensional linear structure written as described above is not washed away on the substrate by a SU-8 developer (obtained from MicroChem Corp. (Newton, Massachusetts)) that dissolves the uncured material after writing. It was necessary to fix to. Voxel dimensions correlated with laser beam power, exposure dose, and photosensitivity of the photoinitiator system used.

If the sample stage height is adjusted so that the constriction (or focal plane) of the laser beam exiting the objective lens is at the film / substrate interface (Z _o ), the exposure dose with writing speed and dye concentration will be the threshold If it was within range, the written line survived. If the writing speed was faster than the threshold speed, i.e. if the exposure dose required to cure the film was not reached, even if the written line was fixed on the substrate surface, Did not survive development. The set of surviving lines was examined to determine the threshold writing speed for a given laser power and dye concentration applied to the film.

  On the other hand, when the sample stage is set so that the constriction of the laser beam does not come to the film / substrate interface, the lines written at a given writing speed survive only if the voxel dimensions are large enough ( That is, the exposure dose at the interface still exceeds the threshold dose for the writing speed and dye density used for the film). This has become a simple method of measuring the laser voxel height for the individual films used in Examples 1-6 below.

  Voxel height was determined by examining how many lines survived (out of 15 written) for development. From the surviving line, the difference between the Z of the highest Z line and the Z before the lowest Z line became the voxel height.

  Next, contrast curves (ie plots of voxel dimensions against reciprocal writing speed (seconds per micrometer)) were generated for each of the photoresist compositions of Examples 1-7.

(Examples 1 and 2)
In Example 1, an acrylate photoresist with 0.5 weight percent IRGACURE 369 photoinitiator prepared as described above was used. In Example 2, a methacrylate photoresist with 1.5 weight percent IRGACURE 369 photoinitiator prepared as described above was used. In Examples 1 and 2, a photoresist was coated on a silicon wafer as described above, and the contrast curve of FIG. 6 was generated for each. Examples 1 and 2 were performed in air. The laser power used was 7 and 18 milliwatts (mW) for Examples 1 and 2, respectively. To produce voxel dimensions comparable to the acrylate photoresist of Example 1, the methacrylate photoresist of Example 2 required the use of 1.5 weight percent IRGACURE 369 photoinitiator and a laser power of 18 mW. Please note that. The contrast curves of both Examples 1 and 2 showed areas where contrast was negative (slope <0). For Example 2 (i.e., methacrylate photoresist), the areas of negative contrast are more apparent and observed at higher scan speeds.

(Examples 3 and 4)
Examples 3 and 4 were performed in the same manner as Examples 1 and 2, except that Example 3 provided an acrylate photoresist containing 0.05 weight percent KL 68 photosensitizer and a laser power of 2.5 mW. Used, Example 4 used a methacrylate photoresist containing 0.05 weight percent KL 68 photosensitizer and 25 mW. The contrast curves obtained for Examples 3 and 4 are shown in FIG. Examples 3 and 4 were performed in air. The contrast curves of Examples 3 and 4 were the same as the contrast curves of Examples 1 and 2.

Comparative Example A
Comparative Example A was performed in the same manner as Example 3, except that it was performed under a nitrogen atmosphere. The contrast curves of Example 3 and Comparative Example A are shown in FIG. In Example 3 (performed in air), a negative contrast region was observed, but in Example 5 in nitrogen, a negative contrast region was not observed. The threshold writing speed when exposed in nitrogen was about 4 times higher (lower dose) than when exposed in air.

(Examples 5 to 8)
Examples 5-7 are performed in the same manner as Comparative Example A, except that each photoresist composition contains 0.1 weight percent, 0.5 weight percent, and 1 weight percent phenothiazine inhibitor. Included. Example 8 was performed similarly to Comparative Example A except that the photoresist composition contained 0.25 weight percent TEMPO. Examples 5-8 were performed under a nitrogen atmosphere. The contrast curves of Comparative Example A and Examples 5-7 are shown in FIG. The contrast curves of Comparative Example A and Example 8 are shown in FIG.

Example 9
Example 9 was performed in the same manner as Example 2, except that the photoresist contained 0.1 weight percent MEHQ inhibitor. The contrast curves of Examples 2 and 9 are shown in FIG.

(Example 10)
Example 10 prepares a diluted methacrylate photoresist with 2.5 weight percent IRGACURE 369 photoinitiator by adding 1.2 times its weight of cyclopentanone to the methacrylate stock solution. This was spin-coated on a silicon substrate to obtain a film having a thickness of about 2 micrometers. Spot alignment written by static rays at different exposure times (energy doses) at the film-substrate interface position, below the interface, and above the interface, using Gaussian and Laguerre Gaussian rays respectively. Then, it was carried out under nitrogen and air-dominated environment. Different laser power was applied for different spot arrays. Gaussian rays were obtained from a laser source immediately after the optical component described above, and Laguerre Gaussian rays were obtained by directing Gaussian rays through a VORTEX phase mask (obtained from RPC Photonics Corp. (Rochester, New York)). For Laguerre Gaussian rays, the central intensity was about 1/6 to 1/13 compared to the high intensity ring region.

  When using Gaussian rays in the air, a donut-shaped spot (FIG. 12A) was clearly observed. When Laguerre Gaussian rays were used under the same exposure conditions (same exposure energy in air), the donut shape was not clear (FIG. 12B). The diameter of the spot center hole (or depression) formed by Laguerre Gaussian rays was much smaller than that formed by Gaussian rays. These results are counterintuitive and are consistent with the negative contrast curve results.

  In FIGS. 12A and 12B, the spot array is formed by static light exposure in air at different exposure times at z position (1 μm above the interface), the laser power is 30 mW, and the film thickness is 2 micrometers. And contained 2.5 weight percent IRGACURE 369 photoinitiator added to the methacrylate stock solution. In FIG. 12A, Gaussian ray characteristics were used (exposure times of 2 seconds, 4 seconds, and 6 seconds were used for the first, second, and third lines, respectively). In FIG. 12B, Laguerre Gaussian rays were used (exposure times of 2 seconds, 4 seconds, and 6 seconds were used for the first, second, and third rows, respectively).

(Example 11)
The procedure of Example 1 was repeated except that the concentration of IRGACURE 369 photoinitiator was 1.5 weight percent and the laser power was 2.5 mW. The contrast curve of Example 11 is shown in FIG.

  All patents and publications cited herein are hereby incorporated by reference in their entirety. All examples presented herein are to be considered non-limiting unless otherwise specified. Those skilled in the art can make various modifications and changes to the present disclosure without departing from the scope and spirit of the present disclosure, and the present disclosure is unnecessary for the exemplary embodiments described above. It should be understood that it should not be limited.

Claims (28)

a) providing a light beam, said light beam having a light beam cross-sectional profile comprising an inner region of relatively low light intensity surrounded by an outer region of relatively high light intensity, wherein The inner region and the outer region have the same temporal profile;
b) providing a photocurable composition, the photocurable composition comprising a free radical polymerizable compound, a free radical polymerization inhibitor, and a multiphoton photoinitiator system; ,
c) exposing at least a portion of the photocurable composition to the light beam so that multiphoton absorption of the portion of the light by the multiphoton photoinitiator system is free to at least a portion of the free radical polymerizable compound. Starting radical polymerization, wherein the photocurable composition is irradiated with at least a portion of the inner region of the light beam to cause at least a portion of the photocurable composition to develop. Curing to a threshold level occurs, and by irradiating the photocurable composition to at least a portion of the outer region adjacent to the inner region of the light beam, the photocurable composition is subjected to at least for development. No curing to the threshold level occurs; and
Including methods.   The method of claim 1, wherein the photocurable composition further comprises an organic polymer, and the photocurable composition is substantially non-flowable.   The method according to claim 1 or 2, wherein the outer region of the beam cross-sectional profile is substantially annular.   The method according to claim 1, wherein the light beam includes a Gauss-Laguerre mode laser beam.   The method according to claim 1, wherein the photocurable composition forms a layer, and the layer is disposed on a substrate.   6. Step c) is repeated a plurality of times, and in each iteration, the light beam focuses on various positions within the photocurable composition according to a predetermined pattern. the method of.   The method according to claim 6, wherein the predetermined pattern includes a predetermined pattern variation in each of three dimensions.   8. The method of any one of claims 1-7, further comprising developing at least a portion of the photocurable composition cured in step c) to at least the threshold level for development.   The method according to any one of claims 1 to 8, wherein the free radical polymerization inhibitor comprises a free radical polymerization inhibitor other than molecular oxygen.   10. A method according to any one of claims 1 to 9, wherein the free radical polymerizable compound comprises at least two acryloyl groups. a) providing at least one light beam;
b) a step of providing a photocurable composition, the photocurable composition comprising a compound capable of free radical polymerization, a free radical polymerization inhibitor other than molecular oxygen, a multiphoton photoinitiator system, The free radical polymerization inhibitor is effective in the absence of oxygen, and
c) at least partially curing at least a portion of the photocurable composition by exposing it to at least one of the light beams, whereby multiphoton absorption of a portion of light by the multiphoton photoinitiator system is Initiating free radical polymerization of the free radical polymerizable compound and thereby reducing the degree of curing of at least a portion of the photocurable composition exposed to the light by stepwise increasing the exposure with the light. Wherein the photocurable composition is substantially free of molecular oxygen before the photocurable composition is exposed to the light beam, and
Including methods.   The method of claim 11, wherein the photocurable composition comprises about 0.1 to about 0.75 weight percent of the free radical polymerization inhibitor, based on the total weight of the photocurable composition.   13. A method according to claim 11 or 12, wherein the free radical polymerizable compound comprises at least two methacryloyl groups and the photocurable composition is substantially free of acrylates.   14. A method according to any one of claims 11 to 13, wherein the photocurable composition further comprises an organic polymer and is substantially non-flowable.   15. The method according to any one of claims 11 to 14, wherein the photocurable composition forms a layer and the layer is disposed on a substrate.   16. Step c) is repeated a plurality of times, in each iteration the light rays are focused on various positions within the photocurable composition according to a predetermined pattern. the method of.   The method of claim 16, wherein the predetermined pattern includes a predetermined pattern variation in each of the three dimensions.   18. A method according to any one of claims 11 to 17, further comprising developing at least a portion of the photocurable composition cured in step c) to at least the threshold level for development. a) providing a light beam;
b) providing a photocurable composition, wherein the photocurable composition is:
A compound capable of free radical polymerization;
A type I photoinitiator;
A process comprising a free radical polymerization inhibitor;
c) at least a portion of the photocurable composition is at least partially cured by exposure to the light, whereby multiphoton absorption of a portion of the light by the type I photoinitiator is Initiating free radical polymerization of the polymerizable compound, thereby reducing the degree of curing of at least a portion of the photocurable composition exposed to the light by stepwise increasing exposure to the light; and ,
Including methods.   20. The method of claim 19, further comprising developing at least a portion of the photocurable composition cured in step c) to at least the threshold level for development.   21. The method of claim 19 or 20, wherein the free radical polymerizable compound comprises at least one of a free radical polymerizable acrylate or a free radical polymerizable methacrylate.   The method of claim 21, wherein the free radical polymerizable compound comprises a free radical polymerizable methacrylate.   The type I photoinitiator is substituted or unsubstituted benzoin ether, benzyl ketal, α, α-dialkoxyacetophenone, α-hydroxyalkylphenone, α-dialkylaminoalkylphenone, acylphosphine oxide, acylphosphine, 23. A method according to any one of claims 19 to 22 selected from the group consisting of substituted derivatives and combinations thereof.   24. A method according to any one of claims 19 to 23, wherein the type I photoinitiator comprises 2-benzyl-2- (dimethylamino) -4'-morpholinobutyrophenone.   25. A method according to any one of claims 19 to 24, wherein the photocurable composition further comprises an organic polymer and is substantially non-flowable.   25. A method according to any one of claims 19 to 24, wherein the photocurable composition forms a layer and the layer is disposed on a substrate.   24. Step c) is repeated a plurality of times, and in each iteration, the light beam focuses on various positions within the photocurable composition according to a predetermined pattern. the method of.   28. The method of claim 27, wherein the predetermined pattern includes a predetermined pattern variation in each of the three dimensions.

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